Conveyor belts for a variety of applications are at present almost exclusively manufactured of plasticized polyvinylchloride (PVC) or polyurethanes (TPU) in combination with one or more polyester (PET) or polyamide (PA) fabrics as support. Said belts are primarily used in the food industry and the business/services area.
The manufacture of said belts has up to now been carried out as a straightforward process in which PVC is applied to the base fabric as a plastisol, whereas polyurethanes are applied as powders.
In both cases fusion is achieved at about 200.degree. C. during a short period in an oven, in general less than 1 minute, resulting in a bonding of the produced polymer sheet to the fabric of more than 2 N/mm and preferably of more than 3 N/mm as determined by a T-peel test.
However for reasons of required recyclability of these belts, high dirt pick-up of certain types and restricted use at low temperatures down to -40.degree. C., there has grown a strong need for alternative materials.
Therefore the primary object of the present invention is to provide such alternative conveyor belts, which have to be completely recyclable without any significant charge to environment due to production of toxic byproducts during recycling.
More in particular, the primary object of the invention is to provide such alternative conveyor belts, which are coated on at least one side of the fabric with an adequately bonded polymer layer (i.e. &gt;1.0 N/mm) and preferably &gt;1.3 N/mm, other than the presently used objected ones, and which, moreover, show a lateral stability i.e. a stability perpendicular to the direction of transportation of goods, and required abrasion resistance and hardness of the coating layer.
It will be appreciated that this aim could not be reached by using e.g. EPDM or TPU containing compositions when using the conventional application methods, such as extrusion/coating, or reversed roll-coating.
Moreover, it was generally known that for conventional conveyor belts to be produced from a latex of SBR (random vinyl aromatic/conjugated diene rubber) and fabric, the fabric threads had preferably been precoated with e.g. a resorcinol-formaldehyde latex, in order to obtain sufficient adhesion.
Moreover, it will be appreciated that such SBR or EPDM comprising conveyor belts have to be vulcanized by heat treatment in its final form.